1. Field of the Invention
The present invention relates to an optical device for optical communications, and more particularly to a parallel optical fiber amplifier having a configuration capable of reusing an amplified spontaneous emission (ASE) light as a secondary pumping source.
2. Description of the Related Art
Currently, Er.sup.3+ -doped fiber amplifiers (EDFAs) having a wide gain band have been proposed to increase the capability of wavelength division multiplexed (WDM) systems to meet the continued demand for higher capacity. For the practical systems using such EDFAs, it has been regarded as inevitably necessary to use silica-based EDFAs of a typical C-band (a wavelength band of 1,530 to 1,560 nm) and/or an L-band of long wavelengths (a wavelength of 1,570 to 1610 nm) coupled together in parallel, in spite of the fact that optical fiber amplifiers made of new materials such as tellurite-based EDFAs have been developed.
In association with L-band EDFAs, there are many pending problems to be solved due to a short history in the development of L-band EDFAs. For example, L-band EDFAs have low power conversion efficiency and thus require high-power pumps. Due to such low pumping efficiency of L-band EDFAs, the silica-based optical fiber amplifiers with an L-band EDFA in a parallel configuration have a limitation in its application in the wide bands. In order to improve the power conversion efficiency of L-band EDFAs, the present inventors have developed a technique for reusing the useless amplified spontaneous emission (ASE) light as a secondary pumping source in an EDF region, which is not being pumped by a light source. In accordance with this technique, a considerable improvement in performance is exhibited. This technique is disclosed in Korean Patent Application No. 98-34370.
In association with the reuse of obsolete reverse ASE light, the present inventors have devised a technique for reusing the reverse ASE light, generated in a C-band EDFA, for amplification at L-band EDFA stage, which is applicable to wide-band silica-based optical fiber amplifiers having a parallel connection configuration.